$ \left(\dfrac{25}{49}\right)^{-\frac{1}{2}}$
Answer: $= \left(\dfrac{49}{25}\right)^{\frac{1}{2}}$ Figure out what goes in the blank: $\Big(? \Big)^{2}=\dfrac{49}{25}$ Figure out what goes in the blank: $\Big({\dfrac{7}{5}}\Big)^{2}=\dfrac{49}{25}$ So $\left(\dfrac{25}{49}\right)^{-\frac{1}{2}}=\left(\dfrac{49}{25}\right)^{\frac{1}{2}}=\dfrac{7}{5}$